1. Field of the Invention
The present invention relates to zoom lenses and image pickup apparatuses, and more specifically to a technical field of a zoom lens and an image pickup apparatus having an optical image stabilization function and a small-sized lens configuration with high image quality and high-magnification.
2. Description of the Related Art
In recent years, small-sized image pickup apparatuses such as video cameras and digital video cameras have been common for home use. Such small-sized image pickup apparatuses are particularly desired to be small, taking portability into consideration, and to have high image quality and high magnifications.
To realize size reduction and increase in image quality and magnification of such image pickup apparatuses, it is important to reduce the overall lengths or depths of image-taking lenses, particularly, zoom lenses, to be included in the image pickup apparatuses and to improve the performance of such lenses.
Besides, there has recently been an increasing demand for the optical image stabilization function. To satisfy the demand for the optical image stabilization function as well as the demands for reduced size and increased image quality and magnification, the degree of designing difficulty has become very high.
Under such circumstances, Japanese Unexamined Patent Application Publication No. 2003-228001 discloses an exemplary zoom lens including, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power.
In the zoom lens disclosed in Japanese Unexamined Patent Application Publication No. 2003-228001, the third lens unit includes a lens element having a positive refractive power and a lens element having a negative refractive power. To correct image blurring due to camera shake, the third lens unit is moved in a direction substantially perpendicular to an optical axis.
Thus, according to Japanese Unexamined Patent Application Publication No. 2003-228001, a zoom lens intended for video cameras capable of optical image stabilization is realized.
Another exemplary zoom lens is disclosed in Japanese Unexamined Patent Application Publication No. 2006-23593. The zoom lens includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a positive refractive power.
In the zoom lens disclosed in Japanese Unexamined Patent Application Publication No. 2006-23593, the fifth lens unit includes, in order from the object side to the image side, a positive sub-unit having a positive refractive power and a negative sub-unit having a negative refractive power. To correct image blurring due to camera shake, the positive sub-unit is moved in a direction substantially perpendicular to an optical axis.
Thus, according to Japanese Unexamined Patent Application Publication No. 2006-23593, a zoom lens intended for video cameras capable of optical image stabilization is realized.
In each of the foregoing related-art zoom lenses, a specific lens unit is moved in a direction substantially perpendicular to the optical axis so as to mainly correct image blurring at and near a telephoto end due to camera shake, whereby good imaging and optical performance is realized. The configuration of such a zoom lens is determined such that the above-mentioned image stabilization function and desired optical performance are realized with a reduced size, increased magnification, and so forth.
The zoom lenses disclosed in Japanese Unexamined Patent Application Publications No. 2003-228001 and No. 2006-23593 each include five lens units, thereby realizing high magnification, high image quality, the optical image stabilization function, and good optical performance.
With the introduction of the optical image stabilization function, however, some problems described below have arisen in the related-art zoom lenses disclosed in Japanese Unexamined Patent Application Publications No. 2003-228001 and No. 2006-23593.
Specifically, with the introduction of the optical image stabilization function, the overall sizes of apparatuses including the zoom lenses are increased with image stabilization mechanisms, which is contrary to the idea of reducing the overall sizes of lens barrels, including relevant mechanical components.
Examples of the problems are as follows. In the zoom lens disclosed in Japanese Unexamined Patent Application Publication No. 2003-228001, the third lens unit is moved in a direction substantially perpendicular to the optical axis so as to correct image blurring due to camera shake. In general, a light beam entering the third lens unit tends to have a large diameter, compared with when entering the other lens units excluding the first lens unit. Taking into consideration the movement for image stabilization, the effective diameter of the third lens unit on the surface thereof becomes very large. Consequently, the size of an apparatus including the zoom lens is increased.
In addition, the third lens unit is provided at substantially a central position of the entire lens system in the optical-axis direction and has a strong refractive power. Therefore, when the third lens unit is moved in a direction substantially perpendicular to the optical axis, the position of the light beam on other lens units significantly changes, and the effective diameters of those lens units on the respective surfaces thereof increases. Consequently, the overall size of an apparatus including the zoom lens is increased.
In the zoom lens disclosed in Japanese Unexamined Patent Application Publication No. 2006-23593, the fifth lens unit includes, in order from the object side to the image side, the positive sub-unit and the negative sub-unit so as to correct image blurring due to camera shake, and the positive sub-unit, which is positioned on the object side, is moved in a direction substantially perpendicular to the optical axis. Therefore, spaces for providing image stabilization mechanisms are to be provided on both sides of the positive sub-unit with respect to the optical axis. Consequently, the overall size of an apparatus including the zoom lens is increased.
Moreover, providing the spaces for image stabilization mechanisms on both sides of the positive sub-unit with respect to the optical axis imposes severer restrictions on the optical design. This may deteriorate image quality.
As described above, the zoom lenses disclosed in Japanese Unexamined Patent Application Publications No. 2003-228001 and No. 2006-23593 are disadvantageous in that the overall sizes of apparatuses including the zoom lenses are increased because of the positions of the lens units responsible for optical image stabilization.
The increase in the overall sizes of apparatuses is remarkable in cases where magnification and image quality desired to be realized are high. This severely prevents the realization of a small-sized, high-magnification zoom lens having the optical image stabilization function.